Mobile devices, such as cellular phones, smartphones, and the like, typically connect to macrocell base stations to make calls and/or transfer data. In order to improve cellular coverage and increase network capacity, there has recently been a trend toward placing femtocell access points in locations that traditionally have poor cellular coverage, such as inside homes, offices, and other buildings. A femtocell access point connects to a wired network and provides wireless access for mobile devices.
Femtocell access points are typically required to be synchronized to a system time that is used by other network entities, e.g. macrocell base stations. In systems that use Code Division Multiple Access (CDMA), the synchronization is to a system time that is an absolute reference. The synchronization requirement is stringent for synchronous networks, such as CDMA2000 1x, CDMA2000 Evolution Data Optimized (EV-DO), and the like. For such networks, the notion of system time is particularly relevant. The system time is typically measured by a number of seconds that have elapsed since a time origin, such as a number of seconds that have elapsed since the time origin of Jan. 6, 1980, at 00:00:00 UTC, which is the same time origin used by the global positioning system (GPS).
The synchronization of a femtocell access point with macrocell base stations is important for performing hand-offs of mobile devices from the femtocell access point to other access points or macrocell base stations. Existing synchronization methods suffer from many problems, such as having low accuracy, coverage problems, or high cost.